1. Field of the Invention
The invention is in the field of desulfurizing and improving the combustion and gasification characteristics of coal. Sulfur in coal is a major source of pollutants from a coal-based energy system. The sulfur in coal appears in three main forms: pyritic, organic, and sulfate. In order for a coal-fired power plant to meet the various local and Federal emissions standards on sulfur dioxide (SO.sub.2), a scrubber system presently must be installed. Such a system is massive and costly because it must handle a large volume of effluent gases in order to capture the minor component of pollutants. Thus, there is a major incentive to remove sulfur at the feed end of a coal-fired power plant.
2. Description of the Prior Art
The prior art includes the following patents:
U.S. Pat. No. 739,374 granted to Baker et al described a process of removing impurities, such as iron combined with sulfur, from gold and silver ores by contacting the ore with dry chlorine gas.
U.S. Pat. No. 1,426,054 granted to Estabrooke et al disclosed a process of desulfurizing coke by contacting the coke with chlorine gas in a blast furnace to produce volatile sulfur chloride.
U.S. Pat. No. 2,698,777 granted to Hartwick et al disclosed a process of removing metallic impurities from coal by contacting the coal with chlorine gas at an elevated temperature (1400.degree. C. or higher). The metallic impurities were converted to volatile chlorides.
U.S. Pat. No. 3,926,575 granted to Meyers disclosed a process wherein finely divided coal containing pyrite was reacted with an aqueous solution of sulfur dioxide and hydrochloric acid (HCl).
U.S. Pat. No. 4,054,421 granted to Robinson et al disclosed a process for reducing the sulfur content of char by washing the char with hydrochloric acid followed by treatment with hydrogen gas.
U.S. Pat. No. 4,081,250 granted to Hsu et al described a method of desulfurizing coal at a moderate temperature and atmospheric pressure by the chlorinolysis of moist coal with the assistance of an organic solvent. In this method, chlorine gas was bubbled through a suspension of powered moist coal in methyl chloroform at a temperature of 74.degree. C. and atmospheric pressure for 1 to 4 hours, followed by separation, hydrolysis and thermal dechlorination of the coal.
Finally, U.S. Pat. No. 4,118,200 granted to Kruesi disclosed a process for the desulfurization of inorganic and organic sulfur constituents of coal by treating the coal in a liquid fused salt bath in the presence of chlorine to react the sulfur-containing constituents with chlorine to form chlorides and elemental sulfur. The liquid fused salt bath was comprised of the chlorides of ferric iron, alkali metals, alkaline earth metals, ammonia, and zinc.